package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.Closeable;

import org.apache.lucene.document.Document;
import org.apache.lucene.document.FieldSelector;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.Term;

/**
 * The interface for search implementations.
 * 
 * <p>
 * Searchable is the abstract network protocol for searching. Implementations
 * provide search over a single index, over multiple indices, and over indices
 * on remote servers.
 * 
 * <p>
 * Queries, filters and sort criteria are designed to be compact so that they
 * may be efficiently passed to a remote index, with only the top-scoring hits
 * being returned, rather than every matching hit.
 * 
 * <b>NOTE:</b> this interface is kept public for convenience. Since it is not
 * expected to be implemented directly, it may be changed unexpectedly between
 * releases.
 *
 * @deprecated In 4.0 this interface is removed/absorbed
 * into IndexSearcher
 */
@Deprecated
public interface Searchable extends Closeable {

    /**
     * Lower-level search API.
     * 
     * <p>
     * {@link Collector#collect(int)} is called for every document. <br>
     * Collector-based access to remote indexes is discouraged.
     * 
     * <p>
     * Applications should only use this if they need <i>all</i> of the matching
     * documents. The high-level search API ({@link Searcher#search(Query,int)}) is
     * usually more efficient, as it skips non-high-scoring hits.
     * 
     * @param weight
     *          to match documents
     * @param filter
     *          if non-null, used to permit documents to be collected.
     * @param collector
     *          to receive hits
     * @throws BooleanQuery.TooManyClauses
     */
    void search(Weight weight, Filter filter, Collector collector) throws IOException;

    /** Frees resources associated with this Searcher.
     * Be careful not to call this method while you are still using objects
     * that reference this Searchable.
     */
    void close() throws IOException;

    /** Expert: Returns the number of documents containing <code>term</code>.
     * 
     * @see org.apache.lucene.index.IndexReader#docFreq(Term)
     */
    int docFreq(Term term) throws IOException;

    /** Expert: For each term in the terms array, calculates the number of
     * documents containing <code>term</code>. Returns an array with these
     * document frequencies. Used to minimize number of remote calls.
     */
    int[] docFreqs(Term[] terms) throws IOException;

    /** Expert: Returns one greater than the largest possible document number.
     * 
     * @see org.apache.lucene.index.IndexReader#maxDoc()
     */
    int maxDoc() throws IOException;

    /** Expert: Low-level search implementation.  Finds the top <code>n</code>
     * hits for <code>query</code>, applying <code>filter</code> if non-null.
     *
     * <p>Applications should usually call {@link Searcher#search(Query,int)} or
     * {@link Searcher#search(Query,Filter,int)} instead.
     * @throws BooleanQuery.TooManyClauses
     */
    TopDocs search(Weight weight, Filter filter, int n) throws IOException;

    /**
     * Returns the stored fields of document <code>i</code>.
     * 
     * @see org.apache.lucene.index.IndexReader#document(int)
     * @throws CorruptIndexException if the index is corrupt
     * @throws IOException if there is a low-level IO error
     */
    Document doc(int i) throws CorruptIndexException, IOException;

    /**
     * Get the {@link org.apache.lucene.document.Document} at the <code>n</code><sup>th</sup> position. The {@link org.apache.lucene.document.FieldSelector}
     * may be used to determine what {@link org.apache.lucene.document.Field}s to load and how they should be loaded.
     * 
     * <b>NOTE:</b> If the underlying Reader (more specifically, the underlying <code>FieldsReader</code>) is closed before the lazy {@link org.apache.lucene.document.Field} is
     * loaded an exception may be thrown.  If you want the value of a lazy {@link org.apache.lucene.document.Field} to be available after closing you must
     * explicitly load it or fetch the Document again with a new loader.
     * 
     *  
     * @param n Get the document at the <code>n</code><sup>th</sup> position
     * @param fieldSelector The {@link org.apache.lucene.document.FieldSelector} to use to determine what Fields should be loaded on the Document.  May be null, in which case all Fields will be loaded.
     * @return The stored fields of the {@link org.apache.lucene.document.Document} at the nth position
     * @throws CorruptIndexException if the index is corrupt
     * @throws IOException if there is a low-level IO error
     * 
     * @see org.apache.lucene.index.IndexReader#document(int, FieldSelector)
     * @see org.apache.lucene.document.Fieldable
     * @see org.apache.lucene.document.FieldSelector
     * @see org.apache.lucene.document.SetBasedFieldSelector
     * @see org.apache.lucene.document.LoadFirstFieldSelector
     */
    Document doc(int n, FieldSelector fieldSelector) throws CorruptIndexException, IOException;

    /** Expert: called to re-write queries into primitive queries.
     * @throws BooleanQuery.TooManyClauses
     */
    Query rewrite(Query query) throws IOException;

    /** Expert: low-level implementation method
     * Returns an Explanation that describes how <code>doc</code> scored against
     * <code>weight</code>.
     *
     * <p>This is intended to be used in developing Similarity implementations,
     * and, for good performance, should not be displayed with every hit.
     * Computing an explanation is as expensive as executing the query over the
     * entire index.
     * <p>Applications should call {@link Searcher#explain(Query, int)}.
     * @throws BooleanQuery.TooManyClauses
     */
    Explanation explain(Weight weight, int doc) throws IOException;

    /** Expert: Low-level search implementation with arbitrary sorting.  Finds
     * the top <code>n</code> hits for <code>query</code>, applying
     * <code>filter</code> if non-null, and sorting the hits by the criteria in
     * <code>sort</code>.
     *
     * <p>Applications should usually call {@link
     * Searcher#search(Query,Filter,int,Sort)} instead.
     * 
     * @throws BooleanQuery.TooManyClauses
     */
    TopFieldDocs search(Weight weight, Filter filter, int n, Sort sort) throws IOException;

}
